1. Field of the Invention
This invention relates to a method of filing and reproducing a medical image for reproducing a medical image such as a radiation image as a visible image based on image signals by an image output apparatus and feeding the image signals to an image filing apparatus to file them on a recording medium such as an optical disk.
2. Description of the Prior Art
Many medical images have heretofore been utilized for medical treatment or research in, for example, medical facilities such as hospitals. Most of the medical images are radiation images. In recent years, many computed tomography (CT) images, magnetic resonance (MR) images and the like are also utilized.
The medical images should be stored for investigating changes in diseases or wounds of patients, and it is legally stipulated that the medical images can be stored for a predetermined period. Therefore, in hospitals or the like, the number of stored medical images increases from day to day. The medical images have heretofore been stored in the form of hard copies. However, storage as hard copies requires a large storage space and burdensome operations for control and retrieval of the medical images in hospitals or the like.
Accordingly, in recent years, it has been proposed to employ an electronic filing method in which medical images are retrievably filed as image signals on a recording medium such as an optical disk or a magnetic disk. In the case where the medical images are filed in this manner on the recording medium, the space requirement and the burden of image storage are lightened, and the operation of image retrieval becomes easy and quick. In the case where radiation images are filed as mentioned above, a radiation image recording and reproducing system using a stimulable phosphor sheet as proposed in, for example, U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-11395 may be utilized. Specifically, with the proposed radiation image recording and reproducing system, a radiation image stored on the stimulable phosphor sheet is detected directly as electric signals. Therefore, it is not necessary to generate electric image signals by reading out hard copies of medical images for the purpose of filing. This is very advantageous in practice.
The image signals obtained by an apparatus for reading out the radiation image from the stimulable phosphor sheet, a CT scanner or the like are sent to an image filing apparatus. In general, the image signals are also sent immediately to an image output apparatus and utilized for immediately reproducing the image for use in medical diagnosis.
However, in the case where a medical image is filed and reproduced in the manner as mentioned above, the image quality often differs between the medical image immediately reproduced by use of the image signals obtained by the radiation image read-out apparatus, the CT scanner or the like and the medical image reproduced by use of the same image signals read from the recording medium of the image filing apparatus (the latter reproduction of the medical image will hereinafter be referred to as re-output of the medical image). This is because image processing conditions differ between the case where the medical image is reproduced immediately as mentioned above and the case where the medical image is retrieved and re-output.
The aforesaid problems will hereinbelow be described in detail. In general, before the image signals representing a medical image are sent to the image output apparatus, they are fed to an image processing apparatus and subjected to an image processing such as a gradation processing or a frequency response processing for improving the image quality of the reproduced visible image, particularly for diagnostic efficiency and accuracy. In the case where the medical image is reproduced immediately as mentioned above, the image signals representing the medical image are of course passed through the image processing apparatus. On the other hand, the raw image signals which have not been processed are sent to the image filing apparatus, and are processed later when they are read from the image filing apparatus and used for re-output of the image. Normally, the image processing conditions in the image processing apparatus are adjusted to various values so that optimal values can be selected in accordance with the image recording portion of an object, image recording conditions, for example, radiation energy, radiation dose, the type of a grid or a collimator, the type of the stimulable phosphor sheet, and the like, and/or the purpose of diagnosis. Therefore, the same image processing conditions are not always set for where the medical image is reproduced immediately and for where the medical image is re-output. The image processing conditions are rather set to different values for the two cases.
If the medical image is reproduced into visible images of image qualities that differ between the aforesaid two cases, it is not always possible to take a diagnosis with the visible images, and in the worst case, an incorrect diagnosis is made.